The present invention is directed to data terminal devices and more particularly to the keyboard construction of such devices. With the development of electronic keyboards, it has been necessary to ensure that any liquid spilled on the keyboard be prevented from penetrating the various elements of the keyboard and thereby disable the operation of the terminal device. Examples of electronic keyboards that provide protection to the internal structure of the terminal device can be found in U.S. Pat. No. 4,020,328, which issued in the name of W. R. Bradam, and U.S. Pat. No. 4,066,850, which issued in the same of G. Heys, Jr., both patents assigned to the assignee of the present application. While both of such patents solve the above-cited problem with respect to the keyboard construction as disclosed in the patents, it has been found that in the case of a membrane-type electronic keyboard having a raised portion on which is located the key members there is presented problems with respect to spilled liquids that could not be solved by the teachings of the patents. In particular, it was found that liquid spilled on the surface of the terminal device entered into the interior of the keyboard due to capillary action. In the situation where the membrane keyboard includes a key indicator sheet which is replaceable to change the designation of the keys of the keyboard, the spilled liquid entered into the area between the sheet and the keyboard, thereby swelling the sheet which prevents the sheet from being easily removed from the keyboard.
It is therefore the principal object of this invention to provide an improved electronic membrane type keyboard for use in a data terminal device which will operate successfully in an environment where liquids may accidentally be spilled on the keyboard.
It is a further object of this invention to provide a waterproof keyboard which is simple in construction and therefore low in cost.